This invention relates in general to analyzing hydrocarbon fluids and, more specifically, to an apparatus and method of obtaining information relating to the composition of downhole fluids flowing in a hydrocarbon well using fiber optics.
Hydrocarbon fluids, such as oil and gas, generally are produced by wells drilled into hydrocarbon producing zones. Often there are multiple hydrocarbon producing zones that are traversed by each well. Perforations in the casing at each of the producing zones allow the fluids to enter the borehole, where the fluids can be recovered. Generally, tubing is used within the casing, which tubing extends to near the bottom of the hole. Liquids generally enter the annulus between the tubing and the casing and flow to the surface up the interior of the tubing.
It can be seen that in conventional wells, when multiple zones produce fluids, the fluids from all the zones are mixed together and returned up the tubing to the surface. Thus, while information can be obtained regarding the total production and combined composition of fluid of the well after the fluid exits the tubing at the surface, little information is available about downhole fluid flow or composition in each of several production zones. As such, only the total quantities of gas, water and oil can be measured at the top showing the composite from all the producing zones, and give little or no information on what is being produced from any one of the zones. Also, it can be seen that such information does not give flow details, for example, on sizes of oil drops or gas bubbles.
Therefore, a need has arisen for an apparatus and method for obtaining information regarding the composition of downhole fluids produced from a well. A need has also arisen for such an apparatus and method that allows for the determination of the composition of downhole fluids from individual zones in a well having multiple zones producing into a single tubing string.
The present invention disclosed herein comprises an apparatus and method for obtaining information about the composition of downhole fluids produced into a wellbore by imaging the downhole fluids within the wellbore with optical tomography. Through the imaging process, quantitative values of oil, water and gas are obtained. A determination of the composition of downhole fluids from individual zones producing into a single well may also be obtained using the optical tomography apparatus and method of the present invention.
The tomograph of the present invention, generally utilizes a bundle optical of fibers that pass downhole and are arrayed with ends pointing into a chamber through which the well fluid flows. The optical fibers run from terminations in a downhole optical tomograph chamber, up the wellbore to a surface system. Light is transmitted down one fiber or a bundle of fibers and is introduced into the downhole tomograph chamber. The other optical fibers or bundles of fibers each pick up portions of the light from the optical tomograph chamber and conduct these light portions up to the surface, where the light portions are detected by a number of light detectors. Preferably, the surface system includes a light source that is sequentially introduced into a first bundle of the optical fibers and sent downhole using a commutation process that, in effect, rotates the light introducing fiber around the chamber.
Portions of light sent through the first bundle of optical fibers carry the light source that is then picked up by detecting optical fiber bundles after the light has traveled through the downhole fluid. The proportions of light picked up by the detecting optical fiber bundles are a function of the fluid flowing through the chamber. The resultant light portions may then can be analyzed to produce an image of fluid flowing in the well. The commutation is preferably fast enough that very little movement of the multi phase fluids occurs during a single revolution or scan of the system.
The tomograph can be used, for example, in combination with seal assemblies between the tubing and the casing when multiple producing zones are encountered. Thus, for example, when there are two zones, typically two sets of casing perforations allow fluid to enter the well and be mixed together. However, in one embodiment of this invention, a seal assembly below the upper zone is used to prevent fluid from the upper zone from mixing with that of the lower zone, and an opening is provided through the tubing above the seal assembly, such that fluid from the upper zone enters the tubing above an optical tomograph, and thus does not pass through the tomograph. In this manner, the tomograph can analyze the fluid being produced by the lower zone unmixed with fluid from the upper zone. The combined production can then be measured at the surface, or in another tomograph higher in the tubing with the production of the lower zone subtracted to obtain production information on the upper zone.
The present invention allows the generation of two or three dimensional images of multiple phase flow in oil wells. This invention also allows determination of the production of multiple zones on an individual basis. No down hole electrical power is required, as all such power to the system can be provided by the surface system. Only optical energy need be transmitted downhole, and thus the system is intrinsically safe and does not pose an environmental hazard. No moving parts are required downhole, any commutation of transmitted signal can be handled at the surface.
This invention provides a method and an apparatus for fiber optic tomographic analysis and imaging of fluids. This invention includes a method for providing information on downhole fluids flowing in a hydrocarbon well, utilizing at least one downhole tomograph chamber. Light is introduced into the chamber by an optical fiber bundle, and portions of the light are collected in second and third optical fiber bundles. The collected portions of light are conveyed through the optical fiber bundles to a surface system, where the light is detected to produce signals proportional to the portions of light to provide information on optical properties of downhole fluid flowing in the well.
The invention is also an apparatus for providing information on downhole fluid flowing in a hydrocarbon well. The apparatus utilizes at least three optical fiber bundles having lower terminations in a downhole tomograph chamber in the well, and having upper terminations in a surface system. The surface system contains a light source and at least two light detectors. A commutator in the surface system links the light source, preferably sequentially, to the light introducing optical fiber bundles, and links light detectors to the receiving optical fiber bundles.